Smart PEGylation of trypsin.

Thermoresponsive oligo(ethylene glycol)-based copolymers were investigated for trypsin conjugation. These copolymers have been synthesized by atom transfer radical polymerization of 2-(2-methoxyethoxy)ethyl methacrylate (MEO(2)MA) with oligo(ethylene glycol) methyl ether methacrylate (OEGMA(475), M(n) = 475 g.mol(-1)) at 60 degrees C in the presence of copper(I) chloride and 2,2'-bipyridyl. Two different ATRP initiators, containing succinimidyl ester moieties, were tested, namely, N-succinimidyl-2-bromopropionate and N-succinimidyl-2-bromoisobutyrate. In both cases, ATRP afforded well-defined polymers with a narrow molecular weight distribution and controlled chain-ends. However, the efficiency of initiation of the two initiators was lower than 1 and therefore the formed polymers exhibited a higher than expected mean degree of polymerization. Nevertheless, all types of polymers could be conjugated to trypsin. The conjugation reaction was performed in borax-HCl buffer. Sodium dodecyl sulfate poly(acrylamide) gel electrophoresis (SDS-PAGE) indicated that polymer/enzyme conjugates were obtained in all cases. However, (co)polymers initiated by N-succinimidyl-2-bromopropionate led to the best conjugation results. The formed P(MEO(2)MA-co-OEGMA(475))-trypsin conjugates were found to be thermoresponsive and moreover exhibited a higher enzymatic activity than unmodified trypsin.